Hello and welcome to the community. 
I really hope this part isn’t true. WeMod has state-of-the-art encryption which makes the software impossible to rip. So if you’ve downloaded “WeMod” from any source other than this website, it’s fake and you’re probably infected with shady crap now.
In any case, take a look through this troubleshooting post here, which resolves the issue 99 out of 100 times. It’s usually caused by a security program on your PC or network, amongst other things: I can’t Install WeMod / "There was a error installing the application" - #2 by Ravenfyre.